Diversity, seasonal abundance, and environmental drivers of chaetognath populations in North Inlet Estuary, South Carolina, USA

Zooplankton samples were collected during one tow between 1000 and 14000 hours each month during outgoing mid-tide from November 2019 to November 2020. Tows were carried out horizontally, 20 meters from the marsh bank, parallel to the shore, and in the direction of the ebbing tide. Each tow lasted roughly 5 minutes and covered 200 meters. The tows were conducted aboard a boat with an epibenthic sled equipped with a 365-µm mesh net, a mouth opening of 50 cm wide by 35 cm high, and with a General Oceanics flowmeter attached to the net’s mouth. During the tow, the net mouth was just above the bottom, ~1.5m below the surface water. Surface (~0.5m below surface water) and bottom (~1.5m below surface water) salinity, temperature, and dissolved oxygen were measured from an anchored boat using a YSI Pro 2030 Sonde. Upon collection, samples were immediately preserved in 4% borax-buffered formaldehyde-seawater solution. Samples were then processed in the lab using a dissecting microscope at 10-40X magnification. For samples with high volumes of animals and small detritus, a Folsom splitter was used to subsample. All chaetognaths found were identified to species using Johnson and Allen (2012), and subsequently counted and classified by egg presence. Egg presence was quantified by the visual presence of eggs. If egg presence was visible, then the chaetognath was counted as having eggs present, whereas if no eggs were visible, the chaetognath was classified as having no eggs present.